Apple Mighty Mouse Pairing Issues.

Ok first off I'm really sorry if this is a simple fix, I have read my instructions and searched for a cure but haven't found any answers.

I recently bought a new mighty mouse for my mac as the original one is broken and only works intermittently. I have put new batteries in the new mouse and followed apples pairing instructions but for some reason the computer doesn't pick up on it's presents. (yes I have got my old mouse turned off while trying to pair the new one.)

So anyone know what I need to do to get my new mouse paired and working?